The present invention relates to ink containers for providing ink to inkjet printers. Inkjet printers frequently make use of an inkjet printhead mounted on a carriage that is moved back and forth across print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text. Ink is provided to the printhead by a supply of ink that is either carried by the carriage or mounted to the printing system not to move with the carriage.
For the case where the ink supply is not carried with the carriage, the ink supply can be in continuous fluid communication with the printhead by the use of a conduit to replenish the printhead continuously. Alternatively, the printhead can be intermittently connected with the ink supply by positioning the printhead proximate to a filling station that facilitates connection of the printhead to the ink supply.
For the case where the ink supply is carried with the carriage, the ink supply may be integral with the printhead, whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supply can be carried with the carriage and be separately replaceable from the printhead. For the case where the ink supply is separately replaceable, the ink supply is replaced when exhausted, and the printhead is replaced at the end of printhead life. Regardless of where the ink supply is located within the printing system, it is critical that the ink supply provide a reliable supply of ink to the inkjet printhead.
In addition to providing ink to the inkjet printhead, the ink supply frequently provides additional functions within the printing system, such as maintaining a negative pressure, frequently referred to as a backpressure, within the ink supply and inkjet printhead. This negative pressure must be sufficient so that a head pressure associated with the ink supply is kept at a value that is lower than the atmospheric pressure to prevent leakage of ink from either the ink supply or the inkjet printhead frequently referred to as drooling. The ink supply is required to provide a negative pressure or back pressure over a wide range of temperatures and atmospheric pressures in which the inkjet printer experiences in storage and operation.
One negative pressure generation mechanism that has previously been used is a porous member) such as an ink absorbing member, which generates a capillary force. One such ink absorbing member is a reticulated polyurethane foam which is discussed in U.S. Pat. No. 4,771,295, entitled “Thermal Inkjet Pen Body Construction Having Improved Ink Storage and Feed Capability” to Baker, et al., issued Sep. 13, 1988, and assigned to the assignee of the present invention.
There is an ever present need for ink supplies which make use of low cost materials and are relatively easy to manufacture, thereby reducing ink supply cost that tends to reduce the per page printing costs. In addition, these ink containers should be volumetrically efficient to produce a relative compact ink supply for reducing the overall size of the printing system. In addition, these ink supplies should be capable of being made in different form factors so that the size of the printing system can be optimized. Finally, these ink supplies should be compatible with inks used in inkjet printing systems to prevent contamination of these inks. Contamination of the ink tends to reduce the life of the inkjet printhead as well as reduce the print quality.
Prior solutions for simple, detachable ink reservoirs have been limited to non-pigmented inks, where drying and clogging concerns are much less. Application of pigmented ink, known for better print and image quality characteristics, to existing designs fail due to drying and clogging. As opposed to dye-based ink, pigmented ink has very small solid particles of colorant dispersed within a carrier fluid. When pigmented ink dries, the solid particles fall out of suspension and solidify on any solid surface. Once the particles become bonded to solid surfaces, they do not re-dissolve in the presence of fresh ink. Multiple cycles of drying will continue to build up solid deposits until clogging occurs.